This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-364341, filed on Nov. 30, 2000, and Japanese Application No. 2001-226610 filed on Jul. 26, 2001, the entire contents of which are incorporated herein by reference.
This invention generally relates to a pressure switching mechanism for the operation gas of a pulse tube refrigerator used for cryogenic refrigeration and a pulse tube refrigerator having the same. More particularly, the present invention pertains to a rotary valve unit for achieving high performance cryogenic effects and a pulse tube refrigerator applied therewith.
A known pulse tube refrigerator is disclosed in Cryogenics, Vol. 30 September Supplement (1990), p.262. FIG. 13 shows the structure of the foregoing known pulse tube refrigerator. A pulse tube refrigerator 611 includes a cold head 303, a regenerator 301 has a regenerator port 311 on one end and is in communication with the cold head 303 on the other end, a pulse tube 302 has a pulse tube port 312 on one end and is in communication with the cold head 303 on the other end. A first solenoid valve 701 and a second solenoid valve 702 are positioned in parallel to each other and are connected to the regenerator port 311 of the regenerator 301 via a regenerator line 321. A third solenoid valve 703 is connected to the pulse tube port 312 of the pulse tube 302 via a pulse tube line 322. A compressor unit 100 has an outlet port 111 and an inlet port 112, in which the outlet port 111 is connected to the first solenoid valve 701 via a high pressure line 121 and the inlet port 112 is connected to the second solenoid valve 702 via a low pressure line 122. A reservoir 401 having a reservoir port 411 is connected to the third solenoid valve 703 via a reservoir line 421. The pressure of the outlet port 111 of the compressor unit 100 corresponds to a high pressure PH, the pressure of the inlet port 112 of the compressor unit 100 corresponds to a low pressure PL, and the pressure in the reservoir 401 corresponds to a middle pressure PM. The high pressure PH is determined to be higher than the middle pressure PM and the middle pressure PM is determined to be higher than the low pressure PL.
The operation of the foregoing pulse tube refrigerator 611 will be explained as follows. First, when the first solenoid valve 701 and the second solenoid valve 702 are closed and the pressure in the pulse tube 302 and the regenerator 301 correspond to the low pressure PL of the inlet port 112, the third solenoid valve 703 is opened. The gas in the reservoir 401 is supplied to the pulse tube port 312 of the pulse tube 302, and thus to increase the pressure of the pulse tube 302 and the regenerator 301 from the low pressure PL to the middle pressure PM corresponding to the pressure in the reservoir 401. Then, the third solenoid valve 703 is closed.
Second, the first solenoid valve 701 is opened. The high pressure gas with the high pressure PH which is compressed and the heat of which is radiated in the compressor unit 100 is cooled down in the regenerator 301 and supplied to the cold head 303 side of the pulse tube 302 to increase the pressure of the regenerator 301 and the pulse tube 302 from the middle pressure PM corresponding to the pressure of the reservoir 401 to the high pressure PH corresponding to the pressure of the outlet port 111. Then the first solenoid valve 701 is closed.
Third, the third solenoid valve 703 is opened. The gas in the pulse tube port 312 side of the pulse tube 302 is returned to the reservoir 401 to decrease the pressure of the pulse tube 302 and the regenerator 301 from the high pressure PH to the middle pressure PM corresponding to the pressure of the reservoir 401. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes lower than the temperature of the cold head 303 due to the adiabatic expansion. Then, the third solenoid valve 703 is closed.
Finally, the second solenoid valve 702 is opened. The gas is returned to the compressor unit 100 to decrease the pressure of the regenerator 301 and the pulse tube 302 from the middle pressure PM to the low pressure PL corresponding to the pressure of the inlet port 112. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes lower due to adiabatic expansion. The gas with lowered temperature is returned to the compressor unit 100 while cooling down the cold head 303 and the regenerator 301. Then, the second solenoid valve 702 is closed.
The foregoing process is determined as one cycle. By repeating this cycle with a frequency of one to several Hz, a cryogenic temperature is generated at the cold head 303.
According to the pulse tube refrigerator 611, since the pressure in the regenerator 301 and the pulse tube 302 has been increased from the low pressure PL to the middle pressure PM corresponding to the pressure in the reservoir 401 before the first solenoid valve 701 is opened, the loss caused by the differential pressure generated when the high pressure gas with high pressure PH is supplied from the outlet port 111 of the compressor unit 100 to the regenerator 301 and the pulse tube 302 after the first solenoid valve 701 is opened is reduced.
In addition, since the pressure of the regenerator 301 and the pulse tube 302 is decreased from the high pressure PH to the middle pressure PM corresponding to the pressure of the reservoir 401 before opening the second solenoid valve 702, the loss caused due to the differential pressure generated when the gas of the regenerator 301 and the pulse tube 303 is supplied to the inlet port 112 with the low pressure PL corresponding to the pressure of the compressor unit 100 when opening the second solenoid valve 702 is reduced.
Another known pulse tube refrigerator is shown in FIG. 14. A pulse tube refrigerator 612 includes a cold head 303. A regenerator 301 has a regenerator port 311 on one end and is in communication with the cold head 303 on the other end. A pulse tube 302 has a pulse tube port 312 on one end and is in communication with the cold head 303 on the other end. A first solenoid valve 701 and a second solenoid valve 702 are positioned in parallel each other and are connected to the regenerator port 311 of the regenerator 301 via a regenerator line 321. A third solenoid valve 703 and a fourth solenoid valve 704 are positioned in parallel and are connected to the pulse tube port 312 of the pulse tube 302 via a pulse tube line 322. A compressor unit 100 has an outlet port 111 and an inlet port 112 in which the outlet port 11 is connected to the first solenoid valve 701 via a high pressure line 121 and the inlet port 112 is connected to the second solenoid valve 702 via a low pressure line 122. A reservoir 401 has a reservoir port 411 which is connected to the third solenoid valve 703 via a reservoir line 421, and an auxiliary reservoir 402 has an auxiliary reservoir port 412, and the auxiliary reservoir port 412 is connected to the fourth solenoid valve 704 via an auxiliary reservoir line 422. The pressure of the outlet port 111 of the compressor unit 100 corresponds to a high pressure PH, the pressure of the inlet port 112 of the compressor unit 100 corresponds to a low pressure PL, the pressure in the reservoir 401 corresponds to a first middle pressure PM1, and the pressure in the auxiliary reservoir 402 corresponds to a second middle pressure PM2. The high pressure PH is determined to be higher than the second middle pressure PM2, the second middle pressure PM2 is determined to be higher than the first middle pressure PM1 and the first middle pressure PM1 is determined to be higher than the low pressure PL (PM greater than PM2  greater than PM1 greater than PL). The second middle pressure PM2 is determined to be higher than the middle pressure PM of the first known pulse tube refrigerator shown in FIG. 13. The first middle pressure PM1 is determined to be less than the middle pressure PM of the first known pulse tube refrigerator shown in FIG. 13. That is, the second middle pressure PM2 is determined to be higher than the middle pressure PM and the middle pressure PM is determined to be higher than the first middle pressure PM1 (PM2  greater than PM greater than PM1).
The operation of the foregoing known pulse tube refrigerator 612 will be explained as follows. First, when the first solenoid valve 701, the second solenoid valve 702, and the fourth solenoid valve 704 are closed and the pressure in the pulse tube 302 and the regenerator 301 corresponds to the low pressure PL of the inlet port 112, the third solenoid valve 703 is opened. The gas in the reservoir 401 is supplied to the pulse tube port 312 side of the pulse tube 302, thus to increase the pressure of the pulse tube 302 end the regenerator 301 from the low pressure PL to the first middle pressure PM1 corresponding to the pressure in the reservoir 401. Then, the third solenoid valve 703 is closed.
Second, the fourth solenoid valve 704 is opened. The gas in the auxiliary reservoir 402 is supplied to the pulse tube port 312 side of the pulse tube 302 to increase the pressure of the pulse tube 302 and the regenerator 301 from the first middle pressure PM1 corresponding to the pressure of the reservoir 401 to the second middle pressure PM2 corresponding to the pressure of the auxiliary reservoir 402. Then, the fourth solenoid valve 704 is closed.
Third, the first solenoid valve 701 is opened. The high pressure gas with the high pressure PH which is compressed and the heat of which is radiated in the compressor unit 100 is cooled down in the regenerator 301 and supplied to the cold head 303 side of the pulse tube 302 to increase the pressure of the regenerator 301 and the pulse tube 302 from the second middle pressure PM2 corresponding to the pressure of the auxiliary reservoir 402 to the high pressure PH corresponding. to the pressure of the outlet port 111. Then, the first solenoid valve 701 is closed.
Fourth, the fourth solenoid valve 704 is opened. The gas of the pulse tube port 312 side of the pulse tube 302 is returned to the auxiliary reservoir 402 to decrease the pressure of the pulse tube 302 and the regenerator 301 from the high pressure PH corresponding to the pressure of the outlet port 111 of the compressor unit 100 to the second middle pressure PM2 corresponding to the pressure of the auxiliary reservoir 402. In this case, the gas temperature of the cold head 303 side of the pulse tube 302 becomes lower than the temperature of the cold head 303 due to the adiabatic expansion. Then, the fourth solenoid valve 704 is closed. Fifth, the third solenoid valve 703 is opened. The gas in the pulse tube port 312 side of the pulse tube 302 is returned to the reservoir 401 to decrease the pressure of the pulse tube 802 and the regenerator 801 from the second middle pressure PM2 corresponding to the pressure of the auxiliary reservoir 402 to the first middle pressure PM1 corresponding to the pressure of the reservoir 401. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes further lower than the temperature of the cold head 303 due to the adiabatic expansion. Then, the third solenoid valve 703 is closed.
Finally, the second solenoid valve 702 is opened. The gas is returned to the compressor unit 100 to decrease the pressure of the regenerator 301 and the pulse tube 302 from the first middle pressure PM1 to the low pressure PL corresponding to the pressure of the inlet part 112. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes further lower due to the adiabatic expansion. The gas with lowered temperature is returned to the compressor unit 100 while cooling down the cold head 303 and the regenerator 301. Then, the second solenoid valve 702 is closed.
The foregoing process is defined as one cycle. By repeating the cycles with a frequency of one to several Hz, a cryogenic temperature is generated at the cold head 303. According to the pulse tube refrigerator 612, since the pressure in the regenerator 301 and the pulse tube 302 has been increased to the second middle pressure PM2 corresponding to the pressure in the auxiliary reservoir 402 before the first solenoid valve 701 is opened, the loss caused by the differential pressure generated when the high pressure gas with high pressure PH is supplied from the outlet port 111 of the compressor unit 100 to the regenerator 301 and the pulse tube 302 after the first solenoid valve 701 is opened is further reduced as compared to the pulse tube refrigerator 611. In addition, since the pressure of the regenerator 301 and the pulse tube 302 is decreased to the first middle pressure PM1 corresponding to the pressure of the reservoir 401 before opening the second solenoid valve 702, the loss caused due to the differential pressure generated when the gas of the regenerator 301 and the pulse tube 302 is returned to the inlet port 112 with low pressure PL of the compressor unit 100 when opening the second solenoid valve 702 is further reduced compared to the pulse tube refrigerator 611.
FIG. 15 shows a further known pulse tube refrigerator disclosed in Advances in Cryogenic Engineering, Vol. 43 (1998) P. 1983. A pulse tube refrigerator 613 includes a cold head 303, a regenerator 301 has a regenerator port 311 on one end and is in communication with the cold head 303 on the other end. A pulse tube 302 has a pulse tube port 312 on one end and is in communication with the cold head 303 on the other end. A first solenoid valve 701 and a second solenoid valve 702 are positioned in parallel with each other and are connected to the regenerator port 311 of the regenerator 301 via a regenerator line 321. A third solenoid valve 703, a fifth solenoid valve 705 and a sixth solenoid valve 706 are positioned in parallel with one another and are connected to the pulse tube port 312 of the pulse tube 302 via a pulse tube line 322. A compressor unit 100 has an outlet port 111 and an inlet port 112, in which the outlet port 111 is connected to the first solenoid valve 701 and the fifth solenoid valve 705 via a high pressure line 121 and the inlet port 112 is connected to the second solenoid valve 702 and the sixth solenoid valve 706 via a low pressure line 122. A reservoir 401 has a reservoir port 411 which is connected to the third solenoid valve 703 via a reservoir line 421. The pressure of the outlet port 111 of the compressor unit 100 corresponds to a high pressure PH, the pressure of the inlet port 112 of the compressor unit 100 corresponds to a low pressure PL, and the pressure in the reservoir 401 corresponds to a middle pressure PM. The high pressure PH is determined to be higher than the middle pressure PM and the middle pressure PM is determined to be higher than the low pressure PL (PH greater than PM greater than PL).
The operation of the pulse tube refrigerator 613 will be explained as follows. First, when the first solenoid valve 701, the second solenoid valve 702, the fifth solenoid valve 705, and the sixth solenoid valve 706 are closed and the pressure in the pulse tube 302 and the regenerator 301 corresponds to the low pressure PL of the inlet port 112, the third solenoid valve 703 is opened. The gas in the reservoir 401 is supplied to the pulse tube port 312 side of the pulse tube 302, thus to increase the pressure of the pulse tube 302 and the regenerator 301 from the low pressure PL to the middle pressure PM corresponding to the pressure in the reservoir 401. Then the third solenoid valve 703 is closed.
Second, the first solenoid valve 701 and the fifth solenoid valve 705 are opened. The high pressure gas with the high pressure PH which is compressed and the heat of which is radiated in the compressor unit 100 is cooled down in the regenerator 301 and supplied to the cold head 303 side of the pulse tube 302 via the pulse tube port 312 side of the pulse tube 302 to increase the pressure of the regenerator 301 and the pulse tube 302 from the middle pressure PM corresponding to the pressure of the reservoir 401 to the high pressure PH corresponding to the pressure of the outlet port 111. The fifth solenoid valve 705 is closed during this process, then the first solenoid valve 701 is closed at the end of this process.
Third, the third solenoid valve 703 is opened. The gas in the pulse tube port 312 side of the pulse tube 302 is returned to the reservoir 401 to decrease the pressure of the pulse tube 302 and the regenerator 301 from the high pressure PH to the middle pressure PM corresponding to the pressure of the reservoir 401. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes lower than the temperature of the cold head 303 due to the adiabatic expansion. Then, the third solenoid valve 703 is closed.
Finally, the second solenoid valve 702 and the sixth solenoid valve 706 are opened. The gas is returned to the compressor unit 100 to decrease the pressure of the regenerator 301 and the pulse tube 302 from the middle pressure PM to the low pressure PL corresponding to the pressure of the inlet port 112. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes further lower due to the adiabatic expansion. The gas with lowered temperature is returned to the compressor unit 100 while cooling down the cold head 303 and the regenerator 301 and is returned from the pulse tube port 312 side of the pulse tube 302 to the compressor unit 100. The sixth solenoid valve 706 is closed during this process, and the second solenoid valve 702 is closed at the end of this process.
The foregoing process is defined as one cycle. By repeating the cycle with a frequency of one to several Hz, a cryogenic temperature is generated at the cold head 303.
According to the pulse tube refrigerator 613, like the pulse tube refrigerator 611, the loss caused due to the differential pressure when the first solenoid valve 701 and the second. solenoid valve 702 are opened is reduced. In addition, since the first solenoid valve 701 is opened while the fifth solenoid valve 705 is still open and the second solenoid valve 702 is opened while the sixth solenoid valve 706 is still open, the heat loss caused by the displacement of the gas in the cold head 303 side of the pulse tube 302 generated when the first solenoid valve 701 and the second solenoid valve 702 are opened is reduced.
FIG. 16 shows a still further known pulse tube refrigerator disclosed in a Japanese patent no. 2553822. A pulse tube refrigerator 614 includes a cold head 303, a regenerator 301 has a regenerator port 311 on one end and is in communication with the cold head 303 on the other end, a pulse tube 302 has a pulse tube port 312 on one end and is in communication with the cold head 303 on the other end. A first solenoid valve 701 and a second solenoid valve 702 are arranged in parallel and are connected to the regenerator port 311 of the regenerator 301 via a regenerator line 321, a third solenoid valve 703, a seventh solenoid valve 707, and a eighth solenoid valve 708 which are positioned in parallel one another and are connected to the pulse tube port 312 of the pulse tube 302 via a pulse tube line 322. A compressor unit 100 has an outlet port 111 and an inlet port 112. The outlet port 111 is connected to the first solenoid valve 701 via a high pressure line 121 and the inlet port 112 is connected to the second solenoid valve 702 via a low pressure line 122. A reservoir 401 has a reservoir port 411 which is connected to the third solenoid valve 703 via a reservoir line 421. A high pressure reservoir 403 has a high pressure reservoir port 413 which is connected to the seventh solenoid valve 707 via a high pressure reservoir line 423, and a low pressure reservoir 404 has a low pressure reservoir port 414 which is connected to the eighth solenoid valve 708 via low pressure reservoir line 424. The pressure of the outlet port 111 of the compressor unit 100 corresponds to a high pressure PH, the pressure of the inlet port 112 of the compressor unit 100 corresponds to a low pressure PL, and the pressure in the reservoir 401 corresponds to a middle pressure PM. The high pressure PH is determined to be higher than the middle pressure PM and the middle pressure PM is determined to be higher than the low pressure PL (PH greater than PM greater than PL). The pressure of the high pressure reservoir 403 is approximately the same as the high pressure PH, and the pressure of the low pressure reservoir 404 is approximately the same as the low pressure PL.
The pulse tube refrigerator 614 corresponds to the pulse tube refrigerator 611 added with the high pressure reservoir 403 and the low pressure reservoir 404 which are connected to the pulse tube port 312 via the seventh solenoid valve 707 and the eighth solenoid valve 708 respectively.
The operation of the pulse tube refrigerator 614 will be explained as follows. First, when the first solenoid valve 701, the second solenoid valve 702, the seventh solenoid valve 707 and the eighth solenoid valve 708 are closed and the pressure in the pulse tube 302 and the regenerator 301 corresponds to the low pressure PL of the inlet port 112, the third solenoid valve 703 is opened. The gas in the reservoir 401 is supplied to the pulse tube port 312 side of the pulse tube 302, thus to increase the pressure of the pulse tube 302 and the regenerator 301 from the low pressure PL to the middle pressure PM corresponding to the pressure in the reservoir 401. Then, the third solenoid valve 703 is closed.
Second, the seventh solenoid valve 707 is opened first, then the first solenoid valve 701 is opened. Along with the supply of the gas of the high pressure reservoir 403 to the pulse tube port 312 side of the pulse tube 302, the high pressure gas with the high pressure PH which is compressed and the heat of which is radiated in the compressor unit 100 is cooled down in the regenerator 301 and supplied to the cold head 303 side of the pulse tube 302 to increase the pressure of the regenerator 301 and the pulse tube 302 from the middle pressure PM corresponding to the pressure of the reservoir 401 to the high pressure PH corresponding to the pressure of the outlet port 111. Then, the first solenoid valve 701 is closed. During this process, the gas supplied from the high pressure reservoir 403 to the pulse tube port 312 side of the pulse tube 302 when opening the seventh solenoid valve 707 is returned to the high pressure reservoir 403 after the first solenoid valve 701 is opened. Then, the seventh solenoid valve 707 and the first solenoid valve 701 are closed.
Third, the third solenoid valve 703 is opened. The gas in the pulse tube port 312 side of the pulse tube 302 is returned to the reservoir 401 to decrease the pressure of the pulse tube 302 and the regenerator 301 from the high pressure PH to the middle pressure PM corresponding to the pressure of the reservoir 401. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes lower than the temperature of the cold head 303 due to the adiabatic expansion. Then, the third solenoid valve 703 is closed.
Finally, the eighth solenoid valve 708 is opened first, then the second solenoid valve 702 is opened. Along with the return of the gas of the pulse tube side port 312 of the pulse tube 302 to the low pressure reservoir 404, the gas is returned to the compressor unit 100 to decrease the pressure of the regenerator 301 and the pulse tube 302 from the middle pressure PM to the low pressure PL corresponding to the pressure of the inlet port 112. In this case, the gas temperature in the cold head 303 side of the pulse tube 302 becomes further lower due to the adiabatic expansion. The gas with lowered temperature is returned to the compressor unit 100 while cooling down the cold head 303 and the regenerator 301. During this process, the gas which is returned from the pulse port 312 side of the pulse tube 302 when the eighth solenoid valve 708 is opened is supplied to the pulse tube port 312 side of the pulse tube 302 after opening the second solenoid valve 702. Then, the eighth solenoid valve 708 and the second solenoid valve 702 are closed.
The foregoing process is defined as one cycle. By repeating this cycle with a frequency of one to several Hz, a cryogenic temperature is generated at the cold head 303.
According to the pulse tube refrigerator 614, like the pulse tube refrigerator 611 the loss caused by the differential pressure generated when the first solenoid valve 701 and the second solenoid valve 702 are opened is reduced. In addition, the heat loss derived from the displacement of the gas in the cold head 303 side of the pulse tube 302 generated when the first solenoid valve 701 and the second solenoid valve 702 are opened is reduced.
Proceedings of the 1998 Meetings of Refrigeration Commission, Cryogenic Association of Japan (1999) p.8 discloses a pulse tube refrigerator which realized the pulse tube refrigerator 614 by replacing the pressure switching mechanism including the first solenoid valve 701, the second solenoid valve 702, the third solenoid valve 703, the seventh solenoid valve 707 and the eighth solenoid valve 708 with a rotary valve unit. FIG. 17 shows the rotary valve unit and the pulse tube refrigerator applied therewith.
A rotary valve unit 211 includes a first valve seat 1, a first valve element 2, a second valve seat 3, a second valve element 4, a motor (not shown), and a housing (not shown) for accommodating the aforementioned members. The first valve seat 1 is fixed to the housing. As shown in FIG. 17, two first output passages 12 which are positioned symmetrical to the rotation axis are formed on the first valve seat. The first output passages 12 are in communication with a regenerator port 311 of a regenerator 301 via a regenerator line 321 and a first output port 63.
The first valve element 2 contacting the first valve seat 1 is fixed to a shaft (not shown) of the motor. As shown in FIG. 17, two high pressure grooves 22 which are recessed by a predetermined depth in the radial direction from the circumference are formed having rotational symmetry along the axis. A low pressure groove 23 recessed by a predetermined depth from the center in the radial direction is formed at a right angle relative to the high pressure grooves 22. An outlet port 111 of a compressor unit 100 is in communication with the high pressure grooves 22 via a high pressure line 121 and a high pressure input port 61. An inlet port 112 of the compressor unit 100 is in communication with the low pressure groove 23 via a low pressure line 122 and a low pressure input port 62.
The second valve seat 3 is fixed to the housing. As shown in FIG. 17, the second valve seat 3 is formed with a second output passages 32 in the center. The second output passages 32 is in communication with a pulse tube port 312 of a pulse tube 302 via a pulse tube line 322 and a second output port 64. Two middle pressure passages 33, two auxiliary high pressure passages 36, and two auxiliary low pressure passages 37 are formed having rotational symmetry along an axis respectively on a common pitch circle on the second valve seat 3. A reservoir port 411 of a reservoir 401 is in communication with the middle pressure passages 33 via a reservoir line 421 and a middle pressure input port 65. A high pressure reservoir port 413 of the high pressure reservoir 403 is in communication with the auxiliary high pressure passages 36 via a high pressure reservoir line 423 and an auxiliary high pressure port 67. A low pressure reservoir port 414 of a low pressure reservoir 404 is in communication wit the auxiliary low pressure passages 37 via a low pressure reservoir line 424 and an auxiliary low pressure port 68.
The second valve element 4 contacting the second valve seat 3 is fixed to the shaft of the motor. As shown in FIG. 17, radial directional long groove 47 recessed by a predetermined depth from the center in the radial direction is formed on the second valve element 4.
The first valve element 2 and the second valve element 4 are pushed towards the first valve seat 1 and the second valve seat 3, respectively, by the pressure of the high pressure gas around the first valve element 2 and the second valve element 4 supplied to a high pressure groove of the first valve element 2.
The rotary valve unit 211 is generally actuated by the motor. When the shaft of the motor is rotated, the first valve element 2 slidably rotates in the direction shown with an arrow in FIG. 17 relative to the first valve seat 1, and the second valve element 4 is slidably rotated in the direction shown with an arrow in FIG. 17. Thus, the same operation as with the pulse tube refrigerator 614 can be achieved by the pulse tube refrigerator 624.
In the known pulse tube refrigerators 611, 612, 613 and 614, the first solenoid valve. 701, the second solenoid valve 702, the third solenoid valve 703, the fourth solenoid valve 704, the fifth solenoid valve 705, the sixth solenoid valve 706, the seventh solenoid valve 707 and the eight solenoid valve 708 which are used for switching the pressures generally include a solenoid coil for generating a magnetic field during energization, a movable metal core actuated by the magnetic force of the magnetic field, a valve seat that the movable metal core contacts and separates from, a coil spring for biasing the movable metal core towards the valve seat when deenergized, and a housing for accommodating the aforementioned members. The solenoid valve with the foregoing structure generates noise when the movable metal core collides with the housing in accordance during opening operation. Thus a loud noise is generated when a continuous operation for opening and closing the several solenoid valves are performed at one to several Hz. When the continuous operation is performed at one to several Hz, operation abnormalities are soon caused due to the fatigue of the coil spring and the heat of the solenoid coil portion. In addition, the movable metal core and the housing are worn due to the sliding of the movable metal core in the housing, and metal particles are generated to contaminate the compressor unit and the cooling unit. Particularly, contamination by the metal particles in the compressor unit causes critical breakdown of the compressor unit. Accordingly, the known pulse tube refrigerators 611, 612, 613 and 614 have drawbacks concerning the noisiness and low durability of the solenoid valves 701, 702, 703, 704, 705, 706, 709 and 708 used for switching the pressure.
On the other hand, since the rotary valve unit 211 supplied to the pulse tube refrigerator 624 operates silently because of the sliding valve, the foregoing noise problem is not caused. Also, by using a material with high wear resistance and with low frictional coefficient for the valve seat, the problem of durability is solved.
Ideally, the sliding plane of the valve seat and the sliding plane of the valve element in the rotary valve tightly contact each other so as not to leak gas from the sliding surfaces, a small amount of gas leakage (hereinafter referred as leakage along sliding surfaces) is generated by the differential pressure at the border between the sliding surfaces in actual operation. The equivalent of leakage along sliding surfaces between the sliding surfaces of the rotary valve unit 211 is schematically shown in a pulse tube refrigerator 624a of FIG. 18.
A first restriction 801 is the equivalent of leakage along sliding surfaces from around the first valve element 2 corresponding to leakage at the high pressure grooves 22 of the first valve element 2 towards the low pressure groove 23 of the first valve element 2. A second restriction 811 is the equivalent of leakage along sliding surfaces from around the first valve element 2 corresponding to leakage at the high pressure grooves 22 of the first valve element 2 towards the first output passages 12 of the first valve seat 1. A third restriction 812 is the equivalent to the leakage along sliding surfaces from the first output passages 12 of the first valve seat 1 towards the low pressure groove 23 of the first valve element 2. A fourth restriction 821 is the equivalent to the leakage along sliding surfaces from around the second valve element 4 towards the second output passages 32 of the second valve seat 3. A sixth restriction 823 is the equivalent to the leakage along sliding surfaces between the second output passages 32 of the second valve seat 3 and the middle pressure passages 33. A seventh restriction 825 is the equivalent to the leakage along sliding surfaces between the second output passages 32 of the second valve seat 3 and the auxiliary high pressure passages 36. An eighth restriction 826 is the equivalent to the leakage along sliding surfaces between the second output passages 32 of the second valve seat 3 and the auxiliary low pressure passages 37. A ninth restriction 831 is the equivalent to the leakage along sliding surfaces from around the second valve element 4 towards the middle pressure passages 33 of the second valve seat 3. An eleventh restriction 851 is the equivalent to the leakage along sliding surfaces from around the second valve element 4 towards the auxiliary high pressure passages 36 of the second valve seat 3. A twelfth restriction 861 is the equivalent to the leakage along sliding surfaces from around the second valve element 4 to the auxiliary low pressure passages 37 of the second valve seat 3.
The fourth restriction 821 is in communication with the second output port 64 and a high pressure input port 61. The sixth restriction 823 is in communication with the second output port 64 and with the high pressure input port 61 via the ninth restriction 831. The seventh restriction 825 is in communication with the second output port 64 and with the high pressure input port 61 via the eleventh restriction 851. The eighth restriction 826 is in communication with the second output port 64 and with the high pressure input port 61 via the twelfth restriction 861. Thus, all restrictions in communication with the output port 64 are in communication only with the high pressure input port 61. Accordingly, only flow of the leaked gas from the high pressure input port 61 to the second output port 64 is generated in accordance with the leakage along sliding surfaces corresponding to each restriction. On the other hand, since it is considered that the resistance of the second restriction 811 and the third restriction 812 are approximately the same, the leaked gas amount from the high pressure input port 61 to the first output port 63 due to the leakage along sliding surfaces and the leaked gas amount from the first output port 63 to the low pressure input port 62 due to the leakage along sliding surfaces are balanced. Because the gas pressure is balanced, the amount of the flowing gas is balanced. Accordingly, in the rotary valve unit 211, a flow of the gas leakage from a pulse tube port 312 of a pulse tube 302 to a regenerator port 311 of a regenerator 301 via a cold head 303 (hereinafter referred as unidirectional flow) is generated due to the leakage along sliding surfaces. Since heat is introduced from the pulse tube port 312 side to the cold head 303 via the pulse tube 302 in accordance with this unidirectional flow, the refrigeration capacity of the pulse tube refrigerator 624 is significantly deteriorated. Accordingly, even when the rotary valve unit 211 is used as the pressure switching mechanism instead of the known pulse tube refrigerators 611, 612, and 613, the refrigeration capacity may be significantly deteriorated compared the known pulse tub e refrigerator 624 having the rotary valve unit 211.
A need therefore exists for a rotary valve unit and a pulse tube refrigerator which is sufficiently quiet and durable, and restricts the generation of unidirectional flow for achieving high refrigeration efficiency.
In light of the foregoing, the present invention provides a rotary valve unit which includes a housing which has a high pressure input port in communication with an outlet port of a compressor unit, a low pressure input port in communication with an inlet port of the compressor unit, a first output port in communication with a regenerator, a second output port in communication with a pulse tube, and a middle pressure input port in communication with a reservoir. The rotary valve unit further includes a first rotary valve which has a first valve seat with a first sliding plane and a first valve element wit h a second sliding plane opposing to and contacting the first sliding plane. T he second sliding plane slidingly rotates relative to the first sliding plane by a rotation of the first valve element relative. to the first valve seat for establishing and interrupting communication between the high pressure input port and the first output port and for establishing and interrupting a communication between the low pressure input port and the first output port. The rotary valve unit further includes a second rotary valve which has a second valve seat with a third sliding plane and a second valve element with a fourth sliding plane opposing to and contacting the third sliding plane. The fourth sliding plane slidingly rotates relative to the third sliding plane by the rotation of the second valve element relative to the second valve seat for establishing and interrupting communication between the second output port and the middle pressure input port. Further, the rotary valve unit includes a motor disposed in the housing and having a shaft for synchronously rotating the first valve element and the second valve element, a recessed space formed in sliding surfaces between the third sliding plane and the fourth sliding plane, and a communication passage for communication between the recessed space and the low pressure input port.
According to another aspect of the invention, a pulse tube refrigerator includes a compressor unit in communication with the rotary valve unit, a regenerator in communication with the rotary valve unit, a pulse tube in communication with the rotary valve unit, a reservoir in communication with the rotary valve unit, and a rotary valve unit which has a housing having a high pressure input port in communication with an outlet port of the compressor unit, a low pressure input port in communication with an inlet port of the compressor unit, a first output port in communication with a regenerator, a second output port in communication with the pulse tube and a middle pressure input port in communication with the reservoir. The pulse tube refrigerator further includes a first rotary valve which has a first valve seat with a first sliding plane and a first valve element with a second sliding plane opposing to and contacting the first sliding plane. The second sliding plane slidingly rotates relative to the first sliding plane by a rotation of the first valve element relative to the first valve seat for establishing and interrupting communication between the high pressure input pert and the first output port and for establishing and interrupting communication between the low pressure input port and the first output port. The pulse tube refrigerator still further includes a second rotary valve which has a second valve seat with a third sliding plane and a second valve element with a fourth sliding plane opposing to and contacting the third sliding plane. The fourth sliding plane slidingly rotates relative to the third sliding plane by the rotation of the second valve element relative to the second valve seat for establishing and interrupting communication between the second output port and the middle pressure input port. Further, the pulse tube refrigerator includes a motor disposed in the housing, the motor comprising a shaft for synchronously rotating the first valve element and the second valve element, a recessed space formed in sliding surfaces between the third sliding plane and the fourth sliding plane, and a communication passage for communication between the recessed space and the low pressure input port.